Car stalling while coming to a stop
 

I have just recently finished installing my turbo kit. So far it drives quite well, no real problems why moving with some speed. The problem is when the car is slowing down or comeing to a stop. When i come to a stop at a light or take a corner really slow. The car will lose revs and stalls. I can avoid this by braking early and gradually bringing the revs down. ; which won't stall the car(most the time). The weird thing is that the car idles fine, with an afr of 14.7. Additionally, if I rev the car while it is still and in neutral, it will also stall after the revs go down. Can someone help me troubleshoot this? I've heard it could be the plugs, which doesn't really make sense but I bought some new ones already. I could the IAC valve or I might have a vacuum leak. Where is the best place to start? Or this is just a problem with the Miata and I'll just have to deal with it.

I am currently running a DIY turbo set up on my 1996 at 8 psi of boost with a lightweight flywheel, which I bet has to do something with it

What kind of ECU are you using? Do you have access to take a log and post your tune? That would help us a lot. I am guessing it’s a standalone. If so, then this is pretty typical when switching out to a lightweight flywheel. Do your homework, but I believe what you want to do is a combination of increasing your dashpot adder and maybe add some more initial duty to your closed loop settings so it “catches” your decreasing RPM better.

Sorry i forgot to mention. Im running a AEM FIC, which is a piggy back. I know it is pretty primitive compared to MS. It has fuel maps, ignition retarding, maf maps and o2 maps, and other basic things. In general should i mess with the maf maps since the car uses the maf when idling?

UPDATE: I installed new spark plugs, and adjusted the idle speed, just a little bit. I can know rev it to around 5.5k in neutral and it won't stall. it still bogs after but doesn't stall. I wouldn't have thought it to be the spark plugs, but I bet changing them and maybe the wires would make a huge difference.

The problem is back and I don't know why. I've clean the throttle body and IAC valve, but it didn't help. If anyone knows a fix, it would be much appreciated.

without the ability to log you'll need to spend a fair bit of time doing it the old fashioned way.

repeat the issue and watch the AFRs while it does it.

hopefully you'll see a pattern in what the AFR does just before stalling.



Otherwise, pretty sure the NA has a physical dashpot.
Is it actually working? is it adjusted right?

the dashpot is essentially a little plunger that the throttle hits a little bit before fully closed, the dashpot is damped so that the throttle closes those last few degrees more slowly than it would otherwise.
Which lets the idle valve etc catch up and take over.

I have a 96 1.8, and they don't come with a dashpot for some reason. It doesn't make sense that it doesn't.

The IAC valve is operated by the ECU to eliminate need for a physical dashpot.

I ran the FIC6 for years. It should not have any impact at all on functionality outside of boost.

You still have your MAF, so that would be something I'd check.
You might want to swap out one from a friend's car to see if that makes a difference. Sometimes just cleaning it can help.
The use of high flow oil saturated air filters can dirty up the MAF sensor.

Just another thing to check. Good luck.

For some reason it did not process with me that you were using a MAF and FIC. Where is your idle air control valve plumbed in? Is it in the intercooler pipe post intercooler and pre throttle body?

Don't forget the old vacuum line pinched by the clutch/ brake pedal.

I have it plumbed into the piping right before the throttle body, which is post intercooler.

Could you elaborate on this?

Update: I removed my lightweight flywheel(It was a pain, but whatever). The car idles betters but isn't perfect. My thinking was that the stock flywheel has more rotational inertia and would slow the transition between open loop and closed loop. Before, it got o bad that I would try to start the car, and it would stall, but now it started every time. Additionally, I have tested my IAC, but unplugging it while the car is running, and the car would die. So this confirms that my IAC valve works, but i don't know if it is working the best. I haven't cleaned the MAF yet but I will try that soon.

Don't worry about it. You don't have the hose he's talking about since you're on stock ecu.

Hum.... You can log the FIC6. AEMLOG as I recall. It has been a few years.
After re-reading your symptoms, a pinched vacuum line doesn't seem to sync with the timing of your issues.

The MAF and stock ECU will have problems with air fuel management when the throttle is suddenly closed. When the throttle is closed on a stock engine the air mostly stops flowing through the MAF. With the turbo and the volume of air in the intercooler you end up with a delayed stoppage of flow through to the MAF when the throttle is closed creating a metering issue.

If you have a blow off valve this condition will be significantly worse because of the huge volume of air lost and you should do away with it until you have a standalone and are metering without the MAF. This was a known issue 10 years ago when people used piggybacks like the FIC.

Sorry I was wrong. I misunderstood how the FIC6 functions.

SpartanSV, no problem. ;=)

I ran my FIC6 with a M45 super charger, and later on my FM turbo setup.
On the turbo setup, (10 psi) I had my blow off recirculating into the intake elbow.
I vaguely recall having the MAF confused by the extra air. It never caused any
significant issues as the OP is having, but our tuning may have been set up differently.
On my 2000 the process was to brute force the factory ecu into closed loop and add fuel
where needed.
Some years could be set up to function more in sync with the factory ecu.
I do think that Sixshooter is on the right track.

I think this was the main source of the problem. I removed the vacuum line from the intake manifold to the blowoff valve. The car feels much better in general but especially when decelerating. Thanks sixshooter.